1. Field of the Invention
This invention relates to catalysts for treating waste gases comprising nitrogen oxides. More particularly, the invention relates to prolongation in life of catalysts of the type which is very useful when applied to a process of treating waste gases comprising nitrogen oxides (hereinafter referred to simply as NOx) in which after addition of ammonia to the waste gas, NOx in the waste gas is suitably reduced with the catalyst into non-noxious gases.
2. Description of the Prior Art
As is well known in the art, waste gases from combustion furnaces such as large-size boilers for use in electric power plants and boilers for independent electric power plants, incinerators and chemical plants comprise NOx. Air pollution with NOx is one of serious social problems to solve. To this end, there have been developed a number of apparatus for the denitrification of waste gases. At present, selective catalytic reduction processes are predominantly used in which waste gases are treated in the presence of catalysts using ammonia as a reducing agent.
The catalysts used in the denitrifying apparatus should have not only high activity, but also a long-term performance stability.
According to our analysis of catalysts used in practical apparatus and various laboratory tests, it was found that denitrification catalysts deteriorated in performance by accumulation of alkali metal components such as Na and K contained in waste gas dust with an attendant shortage of the catalyst life.